In recent years, increasing emphasis has been placed upon the development of hydrometallurgical processes for the recovery of copper metal from copper bearing materials. The intensification of efforts to provide effective and economical hydrometallurgical processes has stemmed from the increasing concern with the pollution and energy problems which accompany pyrometallurgical and electrolytic processes and with the developing necessity for the recovery of copper values from low copper content sources. Additionally, the application of hydrometallurgical processes enables the avoidance of the high capital investments needed for pyrometallurgical facilities.
In the past a number of hydrometallurgical processes have been suggested for direct production of copper metal without recourse to electrolytic processes. However, none of these has found any widespread acceptance due to various economic and technical problems which accompanied their application in commercial operations. The provision of an effective, economically feasible hydrometallurgical process leading directly to metallic product, therefore, remains a highly desirable objective in the copper industry. It has long been recognised that sulfur dioxide gas which is often produced in excess of requirements in primary producer plants, may be used to reduce copper sulfate to copper metal. However this reduction is accompanied by release of sulfuric acid which seriously reduces the efficiency of recovery of copper. Indeed unless the copper sulfate is alkaline, or contains very low free acid, the unreduced copper content in the raffinate makes the operation uneconomical. Use of neutralising agents such as lime or ammonia lead to unwanted by-products and make recirculation of unrecovered copper to the reduction process impractical. Furthermore the overall acid balance of the process is disturbed and make up acid is needed for other steps of the process to proceed under favorable conditions.
The use of amines in organic solution in a water immiscible diluent as a means of removing acid from aqueous metal bearing solutions is known, however it had previously been the practice to regenerate the amines by contacting the organic with an alkali aqueous solution.